The present invention relates generally to an improved pump having a rotor with radial vanes thereon, and wherein the vanes enclose and/or encapsulate magnetic drive components. The pump of the present invention is particularly useful in transferring fragile and/or aggressive fluids. Examples of fragile fluids include human or animal blood, neither of which can tolerate exposure to unusual impact and/or sheer forces. Aggressive fluids include corrosive or poisonous fluids, as well as fluids which cannot tolerate contamination, or which otherwise may destroy seals and/or bearings to reduce the lifetime and/or longevity of the pump structure. Poisonous fluids, for example, are extremely dangerous if a leak develops. More particularly, the present invention relates to a pump which is bearing and seal-free and wherein during operation, the rotor is dynamically balanced by a combination of hydrodynamic and buoyant forces. The pump of the present invention is particularly adapted for transferring human blood and is capable of creating a flow of such liquids without damaging and/or otherwise adversely affecting the quality of the material being pumped. The rotor employed in the pump of the present invention is rotated electromagnetically by means of an electromagnetic drive system operating in conjunction with an array of permanent magnets enclosed within radial vanes on the surface of the rotor, the drive components being arranged in a brushless motor configuration. Alternatively, a permanent magnet-to-permanent magnet coupling may be employed. As such, the arrangement of the present invention provides a symmetrical arrangement which is capable of achieving relative rotation while at the same time being bearing and seal-free.
In the past, pumps and pumping systems have been designed which have been characterized as being bearing and seal-free. Such systems typically employ magnetic levitation means which is in effect an actual form of bearing, much the same as sleeve bearings, ball bearings, or other friction-inducing bearings. Such arrangements using magnetic bearings, while being operational and functional, may be rendered complex and accordingly require significant number of additional components including magnetic devices, position sensors, and rapid-response magnetic drive means. A number of such patents have been granted in the past, including those to Olsen et al. U.S. Pat. Nos. 4,688,998 and 5,195,877. The apparatus of the present invention, by contrast, is fully bearing and seal-free, with dynamic balance being achieved through a combination of hydrodynamic and buoyant forces. In this connection, the rotor of the pump of the present invention is provided with a symmetrical arrangement of radial vanes which enclose components of the magnetic drive so as to enhance and preserve the dynamic balance.
Among the disadvantages inherent in pumps utilizing friction-reducing bearings include local heat generation such as may occur from the use of ball bearings, friction bearings, sleeve bearings, and the like. Low flow and high pressure may result in local areas due to the use of such structures. In addition, with all such bearing-equipped pumps, a high spring constant is provided wherein a small displacement of the rotor (or impeller) introduces very high forces which can damage or effectively destroy bearings. In addition, different forces are introduced in the structure whenever variations in axial positions occur.
In the present structure, the pump is bearing and seal-free, with the effective low compliance of the rotor allowing for relatively high displacement without the creation of large forces otherwise required to hold the rotor in its predetermined position. In addition, the rotor seeks and finds an equilibrium position during operational rotation, which in certain situations can be off-set from the housing axis in either the rotational or transverse axes. This typically occurs when motion or movement is experienced so that the rotational axis of the pump is altered. For example, rotational movement of the pump housing will be manifested in displacement of the rotational or vertical axis of the rotor. The present arrangement has been found to eliminate the need for a highly precise axis in design, fabrication and operation. The lack of a positionally fixed rotational axis reduces the introduction of large forces which otherwise would be created when the axis of the rotor is shifted away from its normal centrally disposed position.
In the arrangement of the present invention, the pump includes a pumping chamber with a central axis, and with a rotor body being disposed within the chamber for bearing and seal-free rotation therewithin. The rotor has a double or dual-conical configuration which converges toward opposed polar regions, and with the axis of rotation extending between these polar regions. The rotor is further provided with radial vanes extending radially outwardly relative to the axis of rotation. These vanes are utilized to enhance flow, as well as to provide a zone for encapsulation of magnetic drive components. Magnetic drive components are typically arranged symmetrically in axially spaced-apart relationship relative to the transverse axis of the rotor. Fluid inlet ports are arranged in the pumping chamber in oppositely disposed relationship within the chamber, with the fluid being transported or transferred to the inlet port area either externally or internally of the chamber. Except for those occasions when the rotor is displaced, it is normally arranged in coaxial relationship with both the pumping chamber and the fluid inlet ports. The outlet port or ports are arranged generally medially of the chamber, midway between the inlet ports and typically are positioned tangentially of the medial portion of the pumping chamber. In those situations where the axis of rotation of the rotor is arranged along a vertical axis, the dual-conical configuration is such that flow on the outside portion of the rotor proceeds downwardly on the upper portion, and upwardly on the lower portion of the dual-cone rotor.
An example of an external transfer of fluids between the oppositely disposed fluid inlet ports is a fluid transfer line which introduces the fluids at opposite ends of the housing. As an example of an internal transfer, a bore may be provided which extends between opposite ends of the rotor, thereby permitting transfer of fluids internally of the structure.
The term "oppositely disposed inlet ports" is intended to reflect the utilization of fluid introduction at opposite ends of the rotor, and is also intended to include those arrangements wherein all of the fluid being pumped is initially introduced into one polar region of the housing, with the fluid nevertheless being transferred either internally or externally of the housing directly to the oppositely disposed polar region.
The pump shown in the drawings is in operational mode with the rotor spinning about its axis of rotation and with all forces acting on the rotor balanced. In the stationary/non-operational mode with the fluid in the housing, only the buoyant forces are acting on the rotor, and the rotor floats up in the random position. In the stationary/non-operational mode with no fluid in the housing, the rotor is resting on the interior of the housing under gravitational forces.
Levitation of the rotor, as indicated, is achieved by a combination of hydrodynamic and buoyant forces. Briefly, the buoyant component is achieved as a result of careful selection of the rotor density, with the preferred relative density being between about 0.1 and 0.9 of the relative density of the fluid being pumped. In a dynamic and operational mode, the buoyant forces merely become a component of lesser or secondary importance to the more significant and more highly effective hydrodynamic force.
The hydrodynamic force component is achieved as a result of the motion of the fluid as it is being moved through the pumping chamber. As the velocity of the fluid increases, the hydrodynamic forces increase substantially, and with the proper selection of rotor density, the hydrodynamic forces which are created during normal operation result in achieving a precise, steady and controllably repeatable centering of the rotor within the pumping chamber.
The pump structure of the present invention has particular application for transferring fragile and/or aggressive liquids, in particular, for transferring human blood. Since certain components in blood are extremely fragile and are damaged upon exposure to external forces, conventional pumps are simply unsuited for the application. Additionally, conventional seals and/or bearings typically found within conventional pump structures pose substantial and significant threats to cell damage. A further feature of the pump of the present invention rendering the pump well suited for transfer of blood is its essentially friction-free operation. Any frictional force creates the risk of generation of thermal energy, and thus may contribute to heat build-up. Since blood is extremely sensitive to temperature change, particularly any increase in temperature above conventional body temperature, reduction and/or virtual elimination of friction provides significant and substantial advantages.
Since the structure of the present invention does not require bearings, energy consumption is reduced through the elimination of energy losses otherwise occurring in the bearings, including energy lost in contact bearings as well as electrical losses in magnetic bearings. The driving forces for the impeller are located generally in planes closely spaced from and symmetrical to the center of gravity or center of mass of the impeller. This feature results in the creation of a gyroscopic effect of a free-body gyroscope, and the configuration of the present invention is such as to stabilize the impeller when the axis of the housing is rotated relative to the spin axis of the rotor. In other words, the spin axis of the rotor may be altered because of a change-of-position of the housing, and thus the spin axis may not always be about the vertical axis, but can be about the horizontal axis as well. The elimination of shafts, bearings and seals substantially reduces the manufacturing cost of the present pump. Also, the present pump has a virtual unlimited mechanical life under normal conditions. The device of the present invention finds utility for any fluids when economy, longevity, and uninterrupted service are the factors.
In addition to blood pump applications, the device of the present invention finds utility in connection with other fluids as well. Certainly non-delicate fluids may be appropriately treated and/or moved with pump devices of the present invention including the aggressive fluids as discussed hereinabove.
One object of the present invention is to bring the fluid from the opposite inlet regions of the housing to the medial plane of the housing, combine in the medial plane two opposite flows, and deliver the fluid to the outlet port or ports with minimal damage and losses to the fluid being pumped through avoidance of turbulence, flow separation, sharp turns, stagnation, and other undesired conditions. This is achieved by combining the upper and lower pair of respective vanes in the single unit at the outlet region, encapsulating the permanent magnets into the vanes at the outer tips of the vanes, and by moving the electromagnetic drive means from the median plane of the housing and the rotor.